Electronic Design

LIN And CAN Networks Will Expand Automotive Distributed Intelligence

The Local Interconnect Network (LIN) protocol specification provides a low-cost, short-distance, and low-speed network, enabling the implementation of a new level of electronics intelligence in automotive subsystems. LIN operates under a CAN platform, but it doesn't require the robust data rate and bandwidth performance, or the higher cost, associated with CAN.

The typical automobile network is broken up into several subnetworks. These in-clude body control, powertrain, and multimedia networks. Depending on the speed and cost requirements, either CAN or LIN can be implemented.

For example, a powertrain demands significant computational processing speeds. Yet, body electronics is more typically oriented to human-interface speeds, which lend themselves nicely to the 20-kbit/s LIN architecture. Window lifts, door locks, seat positioning, environmental controls, wipers, etc. are all ideal benefactors of a robust LIN implementation where wiring complexity and weight are dramatically reduced, and reliability is significantly enhanced.

LIN is a single-master multislave bus that communicates via a single wire, reducing wiring complexity as well as cost. Because this protocol is self-synchronizing, it allows the slave nodes to run from a low-cost RC oscillator.

LIN and CAN don't compete with each other, but instead complement one another. On the one hand, CAN serves high-speed, error-sensitive needs and operates on a 5-V differential bus. LIN, however, serves low-speed, low-bandwidth requirements on a 12-V single-wire bus.

An interface is necessary between LIN's country roads and CAN's high-speed thoroughfares. A bridge node might consist of a microcontroller with an integrated LIN transceiver combined with a low-cost stand-alone CAN transceiver. This provides the intelligence that's needed to watch both buses and interchange data.

For instance, perhaps temperature information would be required by various systems within the automobile. For this application, indoor and outdoor temperature sensors may be incorporated into a car door's LIN network. The door's master node would place the data onto the CAN bus.

From there, additional slave LIN devices in the rear-view mirror, or a heads-up display, might present the data to the driver, while the environmental control system could use the data to activate the air conditioner or heater and defroster grids.

The CAN specification requirement for node-to-node oscillator tolerances of 1.5% and hardware-based error handling drive node costs up to well over $2.00. But, LiN's tolerances of 15% and the ability to implement its protocol entirely in software are moving node costs below $2.00.

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